just a little followup, i had esp_intr() build a little histogram of
retries (i.e. 'i' in esp.c):

 0 11772
 1 211
 2 6101
 3 718
 4 190
 5 466
 6 313
 7 216
 8 96
 9 76
10 118
11 280
12 631
13 268
14 346
15 384
16 110
17 131
18 50

each 'slot' here, represents delay(500) so it appears that a delay(1000)
would seem to catch of most of the retries.